Circadian (-24 hour) rhythms that are controlled by circadian clocks are found in the physiology and behavior of many organisms including humans and fruitflies. In mammals the sleep-wake cycle is the most obvious example of a circadian rhythm that can have important effects on health, but the regulation of body temperature, heartbeat, blood pressure, endocrine functions, renal activity, and liver metabolism have also been shown to be under circadian regulation. Circadian clocks generate oscillating patterns of transcription that control both the rhythm of the clocks themselves and the output that they produce. It is the goal of this research project to first test on a genome-wide scale which transcripts in the head of adult fruitflies are regulated by circadian clocks and then identify a subset of these transcripts that are involved in the regulation of the rest-activity cycle. DNA microarrays will be used to perform the expression analyses; locomotor activity assays will serve as a phenotypic measure for the rest-activity cycle; and a combination of genetic and molecular techniques will be employed in the functional analysis of candidate regulators of the rest-activity cycle. The comprehensive description of the clock controlled transcripts in Drosophila heads will provide a valuable resource for all future studies on circadian rhythms, whereas the discovery of new mediators of the rest-activity cycle will promote a better understanding of the molecular mechanisms underlying both the rest-activity cycle in fruitfiles and the analogous sleep-wake cycle in mammals.